U.S. Patent Publication No. 2010/0032699 A1 defines a light-emitting diode.
In conventional optoelectronic semiconductor chips, such as, for example, light-emitting diodes (LED), the output emitted by the component changes over its lifetime. For example, LEDs that emit radiation in the red wavelength range typically lose from 5 to 10% of their brightness during the first ten thousand hours of operation.
The term “lifetime” is used in particular to define the period during which the brightness of the emitted radiation of the semiconductor chip falls to a defined fraction of the initial value.
The change in output, especially the loss of output, during operation over the lifetime of the semiconductor chip is also known to the person skilled in the art as the ageing behavior. Ageing effects of such semiconductor chips are based, for example, on defects and imperfections in the semiconductor chip, especially on the density of the defects and the mobility thereof.
Such defects can occur in the crystal during growth or as a result of lattice mismatches between substrate and semiconductor layers, it being possible for the defects to spread out and migrate. In addition, defects may occur that diffuse into the semiconductor layers from the outside, for example, as a result of strains in other layers and assembly-related effects.
Such defects can arise inter alia at boundary faces in the semiconductor chip, such as, for example, between the carrier and the semiconductor layers, where there is a change in the lattice structure between the layers, where there is different doping in adjacent layers or at final semiconductor layers.
Such defects result inter alia in absorption of light, in a leakage current or in a change in or distortion of the lattice structure. This adverse action of the defects is exacerbated by high currents during operation of the semiconductor chips, a high operating temperature, a high photon density, and the like. In particular, the action is intensified by effects that increase the density and mobility. For example, as a result of such action the output over the lifetime of the semiconductor chips is reduced, with the result that disadvantageous ageing effects occur over the lifetime of the semiconductor chips.